Wang et al. SpringerPlus 2013, 2:289 http://www.springerplus.com/content/2/1/289 a SpringerOpen Journal RESEARCH Open Access Ontogenesis from embryo to juvenile and salinity tolerance of Japanese devil stinger Inimicus japonicus during early life stage Youji Wang†, Lisha Li†, Guoqiang Cui and Weiqun Lu* Abstract Embryonic development and morphological characteristics of Japanese devil stinger Inimicus japonicus during early life stage were investigated. Larvae were hatched out 50 h after fertilization at temperature 21°C. Total length of the newly hatched larva was 4.03 mm, the mouth of the larva opened at 3 days after hatching (DAH), and the yolk sac of the larva disappeared at 5 DAH. After hatching, the pectoral fin first developed, then the tail fin, dorsal fin, anal fin and pelvic fin continuously developed, and all fins formed completely at 15 DAH. The metamorphosis was complete at 25 DAH, and the body color and habit of the metamorphosed individuals were different from the larvae. At 30 DAH, the morphology and habit of the juveniles were the same to adults. In order to determine the suitable salinity for larviculture of I. japonicus, salinity tolerance at different early developmental stages was compared in terms of the survival activity index (SAI) and mean survival time (MST). The results indicated that salinity tolerance varied with development stages. The optimum salinity range for newly hatched larvae was 10– 25‰. Larvae showed low tolerance to low salinity (5‰) before the mouth opened, and the suitable salinities for the larvae with open mouth, yolk-sac larvae, post yolk-sac larvae were 10–15‰. The flexion larvae showed a wider salinity tolerance with range of 5–20‰. After metamorphosis, the juveniles showed a preferable adaptability of salinities of 15–20‰. The SAI and MST of individuals at various stages under different salinity conditions were positively correlated. Keywords: Inimicus japonicus; Early development; Morphological characteristics; Larvae; Juvenile; Salinity tolerance Introduction commercially important species to be introduced into The devil stinger Inimicus japonicus, a valuable demersal the aquaculture industry (Takushima et al. 2003; Liu and marine scorpaenid fish, is widely distributed along the Quan 2005; Kadomura et al. 2006; Chen et al. 2009; Kim coastal areas of eastern Asia with depth range 10-200m, et al. 2012). However, the wild population of the devil where salinity fluctuates frequently due to rainfall in stinger has declined rapidly because of overfishing and summer. During its reproductive season, the larvae may habitat destruction, it is urgent to conduct relevant stud- suffer environmental changes severely such as salinity ies on resource conservation and artificial breeding. In fluctuation, but little is known about their salinity toler- China and Japan, some hatcheries have tried to establish ance during their early stage. The devil stinger is one of seed production, but success has not yet been attained the species for which artificial seed production and culti- because of sudden mass mortality during the larviculture vation have been developed along the coastal areas of in recent years (Kim et al. 2012). Rearing conditions, egg China and Japan to increase the harvest yield since the quality, and diseases are suspected as causes for this early 2000s, and it has been considered to be a new (Kadomura et al. 2006). Information regarding its early life history and larviculture, which can provide useful in- formation for developing conservation and management * Correspondence: [email protected] †Equal contributors plans, has not been well reported. There is an urgent College of Fisheries and Life Science, Shanghai Ocean University, Key need for researchers to learn about the larval biology of Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, 999 Huchenghuan Road, Shanghai 201306, China © 2013 Wang et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Wang et al. SpringerPlus 2013, 2:289 Page 2 of 13 http://www.springerplus.com/content/2/1/289 this species, and to provide some useful information to indicated an increase in survival and/or growth at inter- culture this species. mediate salinities (>15 ppt but <30 ppt). Others found There are some studies on reproductive biology and improved growth or survival of larvae at higher salin- osteological development of I. japonicus (Imamura and ities (>34 ppt), such as milkfish Chanos chanos Yabe 1997; Takushima et al. 2003; Nozaki et al. 2003). (Swanson 1996) and southern flounder Paralichthys The reproductive cycle of devil stinger has been investi- lethostigma (Henne and Watanabe 2003; Moustakas gated, and its spawning season is from May to August, et al. 2004). Moreover, no significant differences in with peaks from May to June (Nozaki et al. 2003). Al- growth were observed among different salinities in though attempts have been made to establish seed pro- cobia Rachycentron canadum larvae (Faulk and Holt duction and entire aquaculture process for this species 2006). Thus, results vary among species and across de- (Takushima et al. 2003; Liu and Quan 2005), the tech- velopmental stages. The devil stinger I. japonicus is nique has not been fully developed, and studies on larval known to exhibit surface death from hatching to the ecology are still lacking, especially the salinity tolerance first feeding stage during the process of larval produc- during early life stage has not been elucidated. Sudden tion (Ruttanapornvareesakul et al. 2007), whether salin- mass mortality during the larval rearing stage due to un- ity can affect the survival in this period is still unclear. known causes is a serious problem. Inappropriate rear- In the present study, the embryonic and larval development ing or feeding conditions, defects in egg quality, and of laboratory-reared I. japonicus from egg to juvenile were infectious diseases are suspected as causes of sudden described in detail, major morphological changes during mass mortality (Kim et al. 2012). It is therefore necessary larval development were investigated. In addition, salinity to accumulate fundamental information on the larval tolerance of devil stinger during early life stage was investi- biology of this species in order to establish the technique gated. Survival activity index (SAI) and mean survival time for artificial seed production. (MST) of larvae, which are expressed as functions of toler- Study on early life history characters of fish makes a ance to starvation of larvae (Furuita et al. 2000; Matsuo fundamental key for enabling a closer approach to their et al. 2006), have been used as effective indexes for assess- biology and taxonomy (Meijide and Guerrero 2000; ment of salinity tolerance in larval I. japonicus. Celik et al. 2012). Morphological characteristics are very important as they provide information of life history of fish Materials and methods and critical reference to hatchery production (Martinez Broodstock maintenance and Bolker 2003). In addition, studies on embryonic and Thirty males (body weight 600g ) and thirty females (body larval development of any fish species can be useful in weight 300g ) of I. japonicus were purchased from Ningde directing the husbandry efforts of fish breeder to the spe- Fish market (Ningde, Fujian province), and were used as cific state and requirements of each development stage broodstock in the experiment. They were fed with commer- (Celik et al. 2012). Chen et al. (2009) investigated the feed- cial seawater fish feeds (Guangdong Yuehai Feed Group, ing rhythm and lethal time during starvation of the devil Guangdong, China; Protein: 39%,Fat:5%,Fibre:3%,Ash: stinger I. japonicus. However, detailed study about the em- 15%, Moisture: 10%), three times a day. During broodstock bryonic and larval development of scorpionfish is scarce. culture, water temperature, pH, salinity and DO were mon- In addition, information is lacking concerning ontogeny of itored daily at 21 ± 0.5 °C, 8.0–8.1, 28–30‰ and 7.0–8.0 Japanese devil stinger I. japonicus from egg to juvenile. mg l-1 respectively. The photoperiod was maintained at Salinity plays an important role in embryonic devel- 12L/12D by fluorescent lighting (lights on: 07:00–19:00 opment, yolk sac absorption, larval and juvenile hours). Broodstocks were kept in two 500-l tanks. Female growth Boeuf and Payan (2001). Embryonic and larval spawning was induced by intraperitoneally injecting stages are two sensitive periods during fish life his- luteinizing hormone-releasing hormone analogue (LRHA3) tory, changes in environmental conditions may cause and human chorionic gonadotrophin (HCG). The doses of negative effects on larval development, and inappro- these two hormones for female were 5 μg/kg and 800 IU/ priate culture condition may result in mass mortality kg, and males were injected with half doses of them. of larval fish. Thus it is useful to study the salinity Spawning was observed 50 h after injection. tolerance of fish during early life stages and choose the suitable salinity for larviculture (Boeuf and Payan Observations and measurements of embryos and larvae 2001). Some reports of the effects of salinity on growth Fertilized eggs were collected and incubated in 500-l and survival of larval fish, such as